1917.] NATURAL SCIENCES OF PHILADELPHIA. 301 



body very slightly constricted in front of the posterior margin; 

 peripheral angle obtuse, base of body obliquely flattened or very 

 broadly rounded; aperture holostomous, broadly and obliquely 

 ovate, angulated at the posterior commissure; outer lip thin and 

 simple, slightly patulous in front; inner lip excavated medially, 

 thin and reflected, adnate to the body wall; columella smooth. 



Dimensions. — Altitude 14.7 mm.; maximum diameter 4.1 mm. 



This species is well characterized by its sharply defined axial costae 

 which are crowded on the early whorls of the spire but become more 

 widely spaced on the later volutions, and further, the species is 

 characterized by fine regular pittings in the interspiral spaces. Both 

 Acirsa corrugata and Acirsa microstriata differ from Acirsa cerithi- 

 formis M. and H^^ in the more elongate and slender outline and the 

 details of the external ornamentation. Acirsa corrugata is smaller 

 than Acirsa microstriata and unlike the latter exhibits a well developed 

 axial sculpture over the entire shell. 



The very elegantly ornamented species Scalaria dense-striata 

 Kaunhowen/'' from the Msestrichtian of western Europe is probably 

 a member of the genus Acirsa and may be compared with Acirsa 

 corrugata. 



Genua HEMIACIRSA de Boury. 

 Hemiacirsa cretacea n. sp. PI. XIX, fig. 3. 



Descri-ption. — Shell fairly large for the group, slender, turrited 

 and conical in outline; spire acuminate; spire of the type slightly 

 curved, possibly an individual characteristic due to three accidents 

 in the life of the animal, each of which resulted in the breaking of 

 the shell (as scars on the type specimen show) on the same side of 

 the spire or possibly a specific character of this many-whorled form; 

 whorls flattened, very closely appressed posteriorly, less tightly 

 coiled toward the aperture; whorls twelve and a half on the imperfect 

 type, at least two have been broken away, volutions increasing 

 gradually in size; protoconch unknown; sculpture dominantly axial, 

 axial costse abruptly elevated and subangular on the crests, somewhat 

 flexuous, costae sixteen in number on the body of the type, regularly 

 spaced, persistent from suture to suture on the whorls of the spire, 

 interaxial spaces concave and a little wider than the costae; spiral 

 sculpture subdued but well defined in the interaxial depressions, 



4^ Meek and Hayden, 1876, U. S. Geol. Survey of the Terr., Vol. IX, p. 339, 

 PI. 32, figs. 10, a, b. 



^5 Kaunhowen, F., 1897, Palceontol Abhandl, Neue Folge, Bd. IV, p. 43, Taf . III. 

 Figs. 3, 4. 



